Tetraskelion meteorological element radiation shield



Aug. 3, E954 F. R. BELLAHRE 2,685,202

TETRASKELION METEOROLOGICAL ELEMENT RADIATION SHIELD Filed April 25, 1952 2 sheets-sheet 1 yi mum iRANK R BELLMRE ||||I|||I 3 f5 l' a a ATTORNEYS Aug. 3, 3954 A ERROR 5N VAPOR PRESSURE (MILLIBARS) F. R. BELLAIRE TETRASKELION METEOPOLOGICAL ELEMENT RADIATION SHIELD Filed April 25, A24.952

2 Sheets-Sheet -2 I 2 3 4 VENTILATION (MPH) INVENTOR FRANK R. BE LLAIRE ATTORNEYS Patented Aug. 3, 1954 UNITED STATES PATENT OFFICE TETRASKELION METEOROLOGICAL ELEMENT RADIATION SHIELD (Granted under Title 35, U. S. Code (1952),

sec. 266) 9 Claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to a tetraskelion meteorological element radiation shield and more particularly to a radiation shield embodying a plurality of curved vanes for channelling the flow of air over a psychrometer unit for indicating true air temperature and humidity conditions.

In the past, radiation shields of this character were developed with the view of protecting the meteorological elements oi the psychrometer unit while the ventilation thereof was of only secondary importance, the reason for this being that power was readily available for providing the unit with forced ventilation. The requirement of power to provide such ventilation is a serious disadvantage when it is necessary to obtain recordings of temperature and humidity conditions at a remote area where such power is not available or if it is available, can only be obtained in small amounts.

The primary object of the present invention is the provision of a radiation shield which eliminates the disadvantages known in the prior art by designing the shield in such manner that the psychrometer unit is ventilated by natural con- Vection, the air being made to traverse a path established by the cooperating action ci a plurality of curved vanes located exteriorly of the unit. As a result, the shield of the instant invention can be utilized in remote areas and the circulation of air over the unit is improved over prior practices and in addition to this, the amount of heat absorbed by the unit as a result of radiation from solar and terrestrial sources is reduced to a negligible amount.

Another object is the provision of a shield provided with two decks for housing the wet and dry thermometers of the psychrometer unit.

Still another object of the invention is the incorporation in the shield of a reservoir for supplying water to the wet thermometer.

With these and other objects in view, as will hereinafter more fully appear, and which will be more particularly pointed out in the appended claims, reference is now made to the following description taken in connection with the accompanying drawings in which:

Figure 1 is a perspective view of the radiation shield of the invention.

Figure 2 is a diagrammatic perspective view 2 of the curved vane air dei'lectors employed in the radiation shield.

Figure 3 is a diagrammatic perspective view of a plastic container holding the thermocouple leads and a reservoir.

Figure 4 is a chart showing error in indicated vapor pressure versus ventilation rate.

Referring now to the drawings wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in Figure 1 the general organization of parts comprising the invention. The radiation shield comprises three main sections, namely a metal cone-like hat I0, tetraskelion deck elements I2 comprising dry and wet bulb decks II and I3 and the psychrometer unit I4. The tetraskelion section I2 comprises four spaced parallel metal plates I6, I8, 20 and 22 with plates I8, 20 and 22 having a central aperture therein. Plates It and I8 are separated by four vanes 24, each being a section of a right cylinder whose diameter is equal to the radius of the overall shield plus 1/2 of the radius of the central element or apertured area. As shown in Figure 1, vanes 24 are riveted at 2S to the upper and .lower discs I6 and I8 and are equally spaced at 90 intervals about the flat surface of the plates. In order to prevent solar radiation from eecting the operation of the device, the hat I0 is mounted above the tetraskelion section and held in spaced relation thereto by means of supports 28 riveted at one end to plate I6 and at their other ends to the underside of the hat. The wet bulb deck is the same as that described above for the dry bulb deck and likewise has four curved vanes secured between plates 23 and 22. The vanes on this deck, however, are oriented in opposite directions so as to direct the air ow thereinto in a direction opposite to that for the deck immediately above, the reason being that the air flowing through the alleyways formed by the varies will act thereon in different directions thus precluding the possibility of rotation of the device in the event that it is subjected to strong winds.

The psychrometer unit I4 shown in Figure 3 comprises a closed plastic container Sli having a reservoir 32 therein. The reservoir occupies the major portion of the container and is filled through an aperture 3d, which is also adapted to contain the thermocouple leads, and in order to facilitate the filling operation, a vent cap 3E is removed to vent air from the reservoir as it fills with water. Molded into the center of the container 3l! is a cylindrical disc 38 providing means for receiving thermocouple leads 40 extending between wet thermocouple A2 and terminal posts 43 and for receiving the leads 44 extending between dry thermocouple 46 and terminal posts 4l. The dry therinocouple is supported in a Lucite wafer 4B Whichis held in a fixed position by four stainless steel-bars 50. The Lucite wafer Vis secured between metal plates i8 and 20 and therefore serves the further function of isolating the wet and dry thermocouples in their respective chambers. The thermocouple leads are Vled to the periphery of the reservoir ingrooves milled in the top plate and thence through holes to the terminal posts on the bottom of the reservoir housing. The grooves `are covered .with

transparent cellulose tape to hold the wires in place. rlhe wet thermocouple 62 is covered with synthetic fiber which extends down -into the reservoir to supply the wet thermocouple i2 with the necessary moisture for achieving operation of ithe psychrometer unit.

Figure 4 shows the errorsin vaporpressure as .measured by the psychrometer as a vfunction of ventilation rate. The Vadjustable rate was supplied by a small battery powered centrifugal blowerY and was measured by a hot wire anen'lometer. It was seen thatat 0.5 MJRH., the error in vapor pressure is about 0.1 mb. which corresponds to an error in wet bulb depression of 0.07o C. At rates of l M. P. H. or higher, the error is undetectable. The vapor pressure of the test air was 2.85 mb., .which corresponds to a relative humidity vof 12% at 20 C. This .humidity corresponds to dry desert conditions, which are about as stringent .as any to be en- `countered in normal usage. When thepsychrometer is used in more humid air, the ventilation requirements are vconsiderably reduced. Field tests Were also made on the accuracy of the ,psychrometer. The unit and shield .were mounted on a 6 foot mast and the wet and dry temperatures were compared with those obtained in a mercury psychrometer with forced ventilation. In all `conditions, except nearly flat calm, the values agreed to till C., the latter being the limit of error of the recording instruments as well as the mercury psychrometer. When the wind was virtually zero, the wet bulb readings were variable, averaging about 0.3 Chigh, probably due to moisture pile-up inside the tetraskelion.

To test the efficiency of the unit in shielding the thermocouples from solar radiation, a 3,00 watt Mazda derlector lamp was placed at various elevation angles with respect to the shield and was adjusted to give intensities equivalent to solar radiation. Values of solar intensity versus elevation angle were selected from radiometer readings taken under cloudless desert conditions. The same radiometer was used to adjust the lamp intensitives. Table I shows the temperature rise of a thermocouple in the central area of the shield when the lamp was turned on.

Since no such shield can be very effective in the `absence of ventilation, the tests were run using Ycentral area. ,This characteristic was placed in the central area of the shield .and :another was placed upv/ind of the shield. 'It wasfound that low winds (0 3 M. P. H.) passed through the central area undiminished, but that winds of 20 M. P. H. were reduced 50% in the is actually desirable, since it retards excessive evaporation `from vthe Wet element in high winds and thus extends the operating time of the reservoir.

The basic sensing element for both the wet and dry bulbs consists of a copper-constantan couple. rfhis size wire allows low ventilation for the Wet element vand at the same time ,is .sunlciently rugged for field use. Several types of junctions weretestedto determine which, if any, were most consistent. These were spot welded, flame welded, soft soldered and silver soldered and the junctions were made using identical wire and tested on a potentiometer. The results ci tests run at nine dirlerentvxed temperatures between -20 C. and -l-l" C. showed that a maximum temperature diiierence, at any fixed temperature for all couples, was 0.03o C. thus indicating that the particular type of weld selected is not important. Silver soldered junctions were used because of the lack of oxidation andbecause the couple is mechanically stronger than any of the others.

Obviously various modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed:

1. In combination, a meteorological radiation shield comprising a tetraskelion section having a plurality of vertically spaced parallel plates `forming a first and second horizontal decl; positioned one on top of the other, said plates leaving interconnecting means adapted to allow the passage of air therethrough, a dry bulb centrally positioned in said rst deck, a wet bulb centrally positioned in said second deck, means axially secured to said decks and coupled to said wet bulb for supplying liquid thereto, and a shield surmounting said section and axially secured thereto for protecting same from heat radiation.

2. Incombination, a meteorological radiation shield comprising a plurality of vertically spaced interconnected plates forming a pair of thermocouple receiving decks located one on top of the other, said plates having interconnecting means adapted to allow `the passage of air therethrough, a dry bulb and a Wet bulb respectively positioned centrally in said decks, a heat radiation shield surmounting said plates and secured thereto, liquid .supply means coupled to said plates and connected to vsaid Wet bulb thermocouple for supplying moisture thereto;

a dry bulb positioned centrally in said rst deck through one of said apertures, a wet bulb positioned centrally in said second deck through another of said apertures, a container comprising a hollowed out portion forming a liquid reservoir, said wet bulb having one end extending into said reservoir, means mounting said container centrally beneath said second deck, and a shield surmounting said decks for protecting same from heat radiation.

4. In combination, a meteorological radiation shield comprising a plurality of vertically spaced parallel plates interconnected to form a first deck and a second deck and having centrally located apertures, a plurality of right circular cylinder vane sections equidistantly spaced and arranged between the plates forming said decks adapted to allow the passage of air therethrough, said Vane sections respectively connected to the plates of said rst and second deck, a container centrally attached to the bottom of said lower plate, means mounting a dry bulband a Wet bulb axially on said container to respectively position said bulbs centrally in said first and second decks.

5. In combination, a meteorological radiation shield comprising a plurality of spaced interconnected parallel plates having centrally located apertures and forming a first and second deck each respectively receiving a thermocouple centrally therein, a plurality of curved vanes positioned in said decks for directing the ilow of air therethrough, a container forming a reservoir and having a top cylindrical disc concentrically fixed thereon, said container being adapted to be attached to said decks, means attached to said top cylindrical disc for supporting an insulating wafer, a dry thermocouple held by said wafer and adapted to extend centrally into said first deck, a wet thermocouple positioned below said wafer and adapted to lie centrally in said second deck, said wet and dry thermocouples each having connecting leads, grooves cut into the topsurface of said container for containing the thermocouple leads extending from said wet and dry bulbs, and binding posts mounted on said container for connecting said leads thereto.

6. In combination, a meteorological radiation shield comprising a rst pair of connected vertically spaced plates forming a iirst deck, a second pair of vertically spaced plates forming a second deck located underneath said first deck and coupled thereto, said decks having centrally located apertures, a plurality of curved vanes forming connecting members between the plates of cach of said decks adapted to direct air therethrough, a dry bulb held in the top of said Wafer and positioned centrally in said rst deck, a Wet bulb positioned centrally in said second deck, a Lucite wafer located in the aperture between said rst and second decks and separating the wet and dry bulbs, a plastic container secured to the lower plate of said second deck and having means supporting said Wafer and said wet bulb, a liquid reservoir in said container coupled to said wet bulb for supplying moisture thereto, and a cone-shaped shield surmounting said decks adapted to prevent radiation of heat thereon.

7. In combination according to claim 6 wherein the cone-shaped shield axially surmounts said decks for preventing radiation of heat to said unit.

8. The combination according to claim 15 wherein said curved vanes comprise sections of a right circular cylinder equally spaced about the flat surface of said plates, and means securing one end of each of said vanes at the center of said parallel plates forming said decks and the other end at the periphery of said parallel plates.

9. The' combination according to claim 8 wherein the vanes in said first deck are oriented in opposed relationship with the vanes in said second deck.

References Cited in the iile of this patent UNITED STATES PATENTS OTHER REFERENCES Journal of Research of Nat. Bureau of Standards, vol. 20, June 1938, pp. '740 and 742; Figs.

16 and 18. 

